// ciur.cpp : Defines the entry point for the console application.
//

//#include "stdafx.h"
#include <iostream>
#include <fstream>
using namespace std;

bool prim[2000001] ;

int main()
{
	ifstream f("ciur.in");
	ofstream g("ciur.out");

	int n=0;
	f >> n;
	int k = 0;
	for (int i = 2; i <= n; i++) prim[i] = 1;

	for (int i = 2; i <= n; i++)
	{
		if (prim[i]==1)
		{
			k++;
			for (int j = i+i; j <= n; j=j+i)
			{
				prim[j] = 0;
			}
		}
	}

	g << k;

	f.close();
	g.close();
	return 0;
}